Polygalacturonase inhibitor proteins (PGIPs), also known as polygalacturonase-inhibiting proteins, are plant proteins capable of inhibiting the action of polygalacturonase (PG) enzymes produced by bacterial and fungal pathogens. PGs can be produced by pathogens to degrade the polygalacturonan component of

plant cell walls A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mech ...

. PGIPs are

leucine-rich repeat A leucine-rich repeat (LRR) is a protein structural motif that forms an α/β horseshoe fold. It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine. These tandem repeats common ...

glycoproteins of approximately 360 amino acids in length, and PGIPs may reduce the activity of PGs by one or two orders of magnitude. Both competitive and non-competitive inhibition has been observed for various PGIPs. However, no inhibition of endogenous plant PGs that participate in fruit ripening by PGIPs have been reported. Small

oligosaccharides An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide polymer containing a small number (typically two to ten) of monosaccharides (simple sugar ...

produced from PG activity act as signals for the production of PGIPs within the plant. Despite the fact that most plant PGIPs have similar amino acids sequences, there exists a great deal of specificity between different plant and pathogen pairings. The specificity of the PGIPs for certain pathogenic PGs may significantly contribute to different crops being susceptible or resistant to different bacterial and fungal infections.

Structure

At present only one plant PGIP structure has been experimentally determined. A non-glycosylated version of PGIP-2 from ''

Phaseolus vulgaris ''Phaseolus vulgaris'', the common bean, is a herbaceous annual plant grown worldwide for its edible dry seeds or green, unripe pods. Its leaf is also occasionally used as a vegetable and the straw as fodder. Its botanical classification, alo ...

'' (bean) was successfully crystallized and analyzed by

X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

in 2003. Computational modeling has been used since that time to generate theoretical three-dimensional structures for many commonly researched plants and crops using the bean PGIP-2 structure as a template. Additional research has been done to characterize the glycosylations of various PGIPs, and these have been included in the computational models.PG & PGIP Structural Database, http://www.pg-pgip.info

References

External links

PG & PGIP Structural DatabasePectinase Database
{{Enzyme inhibition Hydrolase inhibitors